1. Field of the Invention
This invention relates to a hatch assembly, particularly for a nuclear fuel transfer tube connecting the containment area of a nuclear reactor with a fuel handling building. The hatch assembly includes a hatch cover arranged at that end of the fuel transfer tube which opens into the refueling cavity of the nuclear reactor in the containment area. The opposite end of the fuel transfer tube which opens into the fuel handling building is controlled by a motor or handwheel operated valve mechanism. When fuel assemblies are to be replaced in the nuclear reactor, operating personnel enter the dry refueling cavity and remove the hatch cover. Subsequently, the refueling cavity is flooded with water to ensure that the entire fuel replacing process both in the containment area and the fuel handling building is carried out under water. Upon completion of the fuel replacing operation, the refueling cavity is drained and subsequently operating personnel reenter the refueling cavity and reinstall the hatch cover on the end of the fuel transfer tube to thus provide a tight seal thereon for the normal operation of the reactor. A nuclear fuel transfer system of this type is disclosed in U.S. Pat. No. 4,053,067 issued Oct. 11, 1977.
2. Description of the Prior Art
According to a first conventional arrangement, the hatch cover is secured to the end of the fuel transfer tube by means of a plurality (for example, twenty) of axially oriented, circumferentially distributed threaded bolts held in the hatch cover along the periphery thereof. The bolts are received in corresponding threaded bore holes provided in a hatch ring or flange at the end of the fuel transfer tube. According to a second conventional latching arrangement, the hatch cover carries a complex latching mechanism including a plurality of radially outwardly and inwardly slidable locking bolts actuated by a single handwheel located in the center of the hatch cover.
Since operating personnel should spend the shortest possible time in the containment area because of the prevailing relatively high radiation field, the possibility for a rapid-action operation of the hatch cover is highly desirable. Further, since much of the space in the vicinity of the end of the transfer tube in the containment area is taken up by the fuel transfer equipment, a small spatial requirement for handling the hatch cover is desirable.
While a hatch cover according to the above-outlined second conventional construction is an improvement over the first prior art construction as concerns the rapidity of operation and a small spatial requirement, such a hatch cover has the drawback that the latching mechanism incorporated therein has a complex and interrelated structure and thus, a malfunction of a single sliding bolt may jam the entire mechanism, necessitating lengthy repair work. Further, particularly because of the rapid operations that have to be carried out, the hatch cover undergoes significantly rough handling and thus the risks of damage to the latching mechanism carried by the hatch cover are high.